Extreme Ultraviolet (EUV, 13.5 nm) imaging technology continues to be the primary option for the 22 nm microelectronics node. However, EUV resist performance remains one of the largest barriers to EUV technology implementation, because it is difficult to simultaneously meet performance targets for resolution, line width roughness (LWR) and sensitivity. For example, low concentrations of acid during imaging will yield rough lines (high LWR), but good sensitivity; high concentrations of acid will give smoother lines, but poor sensitivity. To break through to a new level of performance, new materials must be developed that will make improvements toward one performance target without compromising the performance of the other two.
Photoacid generators have been known in the polymer art for decades. Typical first-generation ionic PAGs are sulfonium and iodonium salts. In an early approach to a deep ultraviolet (DUV or 248 nm) photoresist or a 193 nm photoresist, the PAG is randomly dissolved within the polymer film. The polymer has an ester with a side-chain blocking group (e.g. t-butyl) that can be removed with catalytic acid, yielding a developer-soluble carboxylic acid. The advantage of this approach is that these resists are relatively inexpensive and simple to prepare using standard formulation methods. The resists have high sensitivity because acids are free to diffuse through the film, catalyzing acidolysis reactions (removal of ester blocking group) with large turnover numbers. The disadvantage of this approach is that the acid's rapid diffusion limits the ultimate resolution that can be achieved because the acid can diffuse into the unexposed regions of the resist—blurring the aerial image. In a second approach, for which the monomers of the present invention are useful, the photogenerated acid is bound into the polymer chain. The advantage of this approach is that the resist's resolution will not be limited by acid diffusion. A third approach, for which the monomers of the present invention are also useful, is described in PCT application PCT/US09/34707, filed Feb. 20, 2009. This application describes a resist system based on a polymer with PAG and ester functionality located within the main polymer chain. When the PAG breaks apart photochemically or the ester-linkages break apart by acidolysis, the molecular weight of the polymer decreases, allowing for higher acid diffusion during bake and faster resist dissolution during development. The polymer of PCT/US09/34707 is referred to as a chain scission polyester PAG-polymer (CSP3). With CSP3 the photochemical reaction breaks the polymer chain and produces a polymer-bound acid at a chain end. Then, the photogenerated acid catalyzes the transformation of the ester to the developer-soluble carboxylic acid by once again breaking the polymer chain. The resulting areas of the resist exposed to light and subjected to acidolysis reactions have much lower molecular weight resulting from the chain scission reactions. This provides lower Tg, higher acid diffusion rates, and faster dissolution rates.